1. Field of the Invention
This invention relates to storage facilities and methods for creating these facilities for storing materials such as fluid hydrocarbons in underground caverns created in naturally-occurring geological formations. More specifically, the invention relates to the creation of storage caverns in naturally-occurring substantially horizontal layers of salt deposits.
2. Description of the Related Art
It is known in the art to create storage caverns in large naturally-occurring salt domes for the purpose of storing natural gas and other light hydrocarbons, such as ethane, propane, and butane, as well as crude oil. However, of the naturally-occurring salt formations, salt domes are the exception. By far the majority of salt formations are in the form of salt deposits of a non-domed structure. More typically, these salt deposits may be in the form of layered formations of salt interposed between layers of bed rock or bed rock and overburden. These deposits frequently occur in substantially horizontal layers of varying thickness.
While it is readily apparent that salt domes may be utilized for the creation of storage caverns that are elongate in a vertical direction, for the storage of natural gas, it has not heretofore been known to utilize substantially horizontal layered salt formations for the creation of storage caverns for natural gas or other hydrocarbons. Whereas it may be possible to produce "vertical storage caverns" in layered salt formations, the storage cavern will normally extend through several layers, including layers that are of a nonsalt type and that may be permeable to the hydrocarbon being stored. Thus, there is always the possibility of leakage, especially gas leakage, through intervening layers between the salt layers. If the vertical cavern does not extend through several layers then it is usually too small to be of commercial interest because of the relative shallowness of any one layer of salt.
U.S. Pat. No. 3,873,156 shows the solution mining of layers of salt deposits. The method appears to show a first and second bore and a device, a solvent delivery nozzle, that may be guided horizontally for leaching salt. The method requires drilling two or more bore holes intersecting a bedded salt deposit which includes a "geological anomaly" which prevents the effective coalescing of the bore holes. The salt deposit is hydraulically fractured from one of the bore holes as far as feasible towards the other bore hole. Thereafter, a horizontally extending passageway is solution mined from the lower end of one of the bore holes, through the salt bed and through the geological anomaly, into communication with the hydraulically fractured passageway. This provides a solution mining cavity through which a solvent fluid can be passed from one of the bore holes and withdrawn from the other bore hole in order to enlarge the cavity. However, the means utilized for making the cavern is not a means that provides for controlled leaching of salt but rather a solvent delivery nozzle. Further, there is no indication that the cavern produced is capable of use for storage of fluid materials.
U.S. Pat. No. 2,810,263 is directed to a natural gas storage cavern. From the drawings, the cavern produced appears to be horizontal albeit that the cavern has vertical supports.
U.S. Pat. No. 2,880,587 shows vertical storage caverns that are in communication through a horizontal channel. Again, this is significantly different than producing a horizontally-oriented storage cavern in a layered salt deposit. The patent merely shows how to utilize 2 bore holes (one for pumping in fresh water, the other for removing brine) to cause communication between vertical caverns.
U.S. Pat. No. 3,347,595 also shows how to establish communication between bore holes in solution mining. Again, there is no teaching or suggestion regarding horizontal storage caverns or methods for producing these.
U.S. Pat. No. 3,374,633 discusses underground storage facilities and their construction using first and second bore holes. The method utilizes a solution, which is a non-solvent for the material of the formation (salt) as a fracturing material. Once the material is fractured, a solvent material is injected through one bore hole and concentrated brine removed from the second bore hole. In this way, a storage cavern is formed between the two bore holes, as best illustrated in FIG. 3 of the patent.
Since salt deposits are much more widely distributed across the United States and the world than salt domes, it would be highly desirable if a method could be developed for the creation of storage caverns of commercially useful size in layered salt deposits. Further, the method should produce storage caverns that are stable and useful for the storage of products ranging from natural gas through light hydrocarbons to heavy hydrocarbons, such as crude oil, and other fluids that are not solvents for the salts of the formation